The project includes studies on the structure and mechanism of action of bovine and canine pepsinogens and pepsins, on the process of activation of zymogens, on inhibition of pepsins, and on evolutionary aspects of the structures of acid proteases. BIBLIOGRAPHIC REFERENCES: Oxidation of Methionine Residues of Porcine and Bovine Pepsins. K. Kido and B. Kassell, Biochemistry 14, 631-635 (1975). Inhibitors of Proteolytic Enzymes. Kassell, B. and Williams, M. J., in Handbook of Biochemistry and Molecular Biology, 3rd Ed., G. Fasman, Ed., Vol. II, 611-668 (1976) CRC Press, Cleveland, in press.